Methodology Conditions for the formation of massive seed black holes 1. Major merger (1:3) of gas-rich late-type galaxies (B/T < 0.2) 2. Host halo M h > 10 11 M Sun 3. No a pre-existing black hole of M BH > 10 6 M Sun Friday, August 17, 12
Evolution of the gas component in major merger of disk Friday, August 17, 12
Multi-scale galaxy merger simulations from ~100 kpc to 0.1 pc Mayer et al. 2007, 2008, 2010 Using Smoothed Particle Hydrodynamics (SPH code GASOLINE) + splitting of gas particles (Kitsionas & Withworth 2002, Bromm 2004) to increase mass and spatial resolution as galaxy merger proceeds Max. Resolution 3000 solar masses and 0.1 pc Effective equation of state (EOS) - ideal gas, P = ( γ− 1) ρ ε , varying effective “ γ “ - to model local balance between heating and cooling in nuclear region (based on Spaans & Silk 2000;2005 – steady-state interstellar gas model heated by starburst w/ radiative transfer) 200 kpc 60 kpc EOS stiff (=medium highly pressurized) in the regime of average nuclear disk densities (10 4 -10 5 cm -3 ) due primarily to irradiation by dust grains heated by stellar UV (SFR >~ 30 Mo/yr) Friday, August 17, 12
Multi-scale galaxy merger simulations from ~100 kpc to 0.1 pc Mayer et al. 2007, 2008, 2010 Using Smoothed Particle Hydrodynamics (SPH code GASOLINE) + splitting of gas particles (Kitsionas & Withworth 2002, Bromm 2004) to increase mass and spatial resolution as galaxy merger proceeds Max. Resolution 3000 solar masses and 0.1 pc Effective equation of state (EOS) - ideal gas, P = ( γ− 1) ρ ε , varying effective “ γ “ - to model local balance between heating and cooling in nuclear region (based on Spaans & Silk 2000;2005 – steady-state interstellar gas model heated by starburst w/ radiative transfer) Stiff EOS due to “thermostat” of SF 200 kpc 60 kpc EOS stiff (=medium highly pressurized) in the regime of average nuclear disk densities (10 4 -10 5 cm -3 ) due primarily to irradiation by dust grains heated by stellar UV (SFR >~ 30 Mo/yr) Friday, August 17, 12
SELF-GRAVITATING GAS DISKS: STABILITY and INFLOWS THREE REGIMES: Toomre parameter Q = κ v s / π G Σ Q < 1 locally unstable to collapse - fragmentation on (from linear local dynamical timescale (t dyn ) - gas clumps make stars perturbative analysis of self-gravitating rotating fluid in infinitesimally thin disk) 1 < Q < 2 locally stable, globally unstable to non-axisymmetric modes (spiral modes, bar modes) -- angular momentum transport (on a few t dyn ) via spiral density waves (Lynden Bell & Pringle 1979; Lin & Pringle 1987; Laughlin & Adams 2000) -- gas inflow towards state of minimum energy Q > 2 locally and globally stable - dynamically uninteresting -Sweet spot (1<Q<2): a non-fragmenting globally unstable disk to sustain central gas inflow - The dissipation rate in the system is crucial – if cooling efficient amplitude of non-axisymmetric modes increases - inflow increases but Q <~ 1 approached (Tcool < Tdyn drives Q below 1, while with Tcool > Tdyn self-regulation to Q >~1) Friday, August 17, 12
SELF-GRAVITATING GAS DISKS: STABILITY and INFLOWS 1 < Q < 2 THREE REGIMES: Toomre parameter Q = κ v s / π G Σ Q < 1 locally unstable to collapse - fragmentation on (from linear local dynamical timescale (t dyn ) - gas clumps make stars perturbative analysis of self-gravitating rotating fluid in infinitesimally thin disk) 1 < Q < 2 locally stable, globally unstable to non-axisymmetric modes (spiral modes, bar modes) -- angular momentum transport (on a few t dyn ) via spiral density waves (Lynden Bell & Pringle 1979; Lin & Pringle 1987; Laughlin & Adams 2000) -- gas inflow towards state of minimum energy Review Volonteri 2010 Q > 2 locally and globally stable - dynamically uninteresting Q<1 -Sweet spot (1<Q<2): a non-fragmenting globally unstable disk to sustain central gas inflow - The dissipation rate in the system is crucial – if cooling efficient amplitude of non-axisymmetric modes increases - inflow increases but Q <~ 1 approached (Tcool < Tdyn drives Q below 1, while with Tcool > Tdyn self-regulation to Q >~1) Friday, August 17, 12
SELF-GRAVITATING GAS DISKS: STABILITY and INFLOWS THREE REGIMES: Toomre parameter Q = κ v s / π G Σ Q < 1 locally unstable to collapse - fragmentation on (from linear local dynamical timescale (t dyn ) - gas clumps make stars Evolution of disk gas perturbative analysis of self-gravitating surface density profile rotating fluid in (1 < Q < 2) regime infinitesimally thin disk) 1 < Q < 2 locally stable, globally unstable to non-axisymmetric modes (spiral modes, bar modes) t= a few tdyn -- angular momentum transport (on a few t dyn ) via spiral density waves (Lynden Bell & Pringle 1979; Lin & Pringle 1987; Laughlin & Adams 2000) T=0 -- gas inflow towards state of minimum energy Q > 2 locally and globally stable - dynamically uninteresting -Sweet spot (1<Q<2): a non-fragmenting globally unstable disk to sustain central gas inflow - The dissipation rate in the system is crucial – if cooling efficient amplitude of non-axisymmetric modes increases - inflow increases but Q <~ 1 approached (Tcool < Tdyn drives Q below 1, while with Tcool > Tdyn self-regulation to Q >~1) Friday, August 17, 12
INFLOW BOTTLENECK: COOLING AND FRAGMENTATION In system that cools rapidly (tcool < tdyn) and accumulates gas via inflow eventually Q drops to < 1 and fragmentation/star formation takes over CONVENTIONAL WAY-OUT: SUPPRESS FRAGMENTATION BY SUPPRESSING COOLING (keep T > 10 4 K) - NEED METAL-FREE GAS + H 2 dissociation by Lyman-Werner UV bg above mean cosmic value at z > 2 BUT METAL-FREE GAS UNREALISTIC CONDITION! (a) Metallicity > 10 --5 solar reached at z > 10 - sufficient to trigger rapid cooling esp. in presence of dust (Omukai et al. 2008). (b)Weak inflow rates <1 Mo/yr (Wise et al. 2008; Regan & Haenhelt 2009,2010) Not enough to assemble supermassive clouds/SMS Indeed no self-gravitating compact object forms Metal-free protogalaxy simulation Regan & Haenhelt 2009 Friday, August 17, 12
Formation of supermassive black holes by direct gas collapse in galaxy mergers Lucio Mayer University of Zurich Collaborators: Stelios Kazantzidis (CCAPP Ohio State Univ.) Simone Callegari (Univ. of Zurich) Andres Escala (KIPAC Stanford/UChile) Silvia Bonoli (Univ. Zurich) Friday, August 17, 12
Direct gas collapse model: brief intro Rapid formation of massive BH seed --- mass M BH ~ 10 5 – 10 9 Mo If happens early (z >~ 8-10) can explain high-z QSOs (M BH > 10 9 Mo) without requiring the continuous Eddington accretion needed for <~100 Mo Pop III (Volonteri & Rees 2006) Simulations show Pop III seeds accrete well below Eddington, eg Johnson & Bromm 2006; Wise et al 2008; Milosavljevic et al. 2010) due low density gas plus their own radiative feedback I - Gas inflow in galaxy from kpc to << 1 pc scales to form supermassive gas cloud (M> 10 6 Mo) - need efficient loss of angular momentum in galactic disk gas across many spatial scales (eg Lodato & Natarayan 2006) II - Depending on mass and internal rotation of supercloud (T/W) two pathways: (a) supermassive cloud collapses dynamically and globally into massive black hole with M BH ~ M cloud due to radial GR radial instability (Fowler & Hoyle 1966; Zeldovitch & Novikov 1972; Baumgart & Shapiro 1999; Shibata & Shapiro 2002; Saijo & Hawke 2009) ---> direct formation of SMBH (b) forms a short-lived ( >~ Myr) supermassive star collapsing into BH at the center due to catastrophic neutrino cooling (Begelman et al. 2006; Begelman 2008; Begelman & Volonteri 2010). Even if BH initially only 10-100 Mo it accretes super-Eddington from a pressure-supported convective envelope powered by BH accretion energy (“Quasi-star”) reaching > 10 4-5 Mo before cloud dispersal in a few Myr ---> formation of massive BH seed This talk: how can step (I) be achieved? Friday, August 17, 12
TIMESCALE FOR SUPERMASSIVE CLOUD ASSEMBLY: REQUIRED GAS INFLOW RATE SImple argument: a supermassive star (M star >~ 10 6 Mo) has short lifetime (t life ~ 10 6 yr) must be assembled on t form < t life ---- Characteristic gas inflow rate to feed the cloud dM g /dt > M star /t life > 1 Mo/yr for M star >~ 10 6 Mo (Begelman 2008) Friday, August 17, 12
TIMESCALE FOR SUPERMASSIVE CLOUD ASSEMBLY: REQUIRED GAS INFLOW RATE SImple argument: a supermassive star (M star >~ 10 6 Mo) has short lifetime (t life ~ 10 6 yr) must be assembled on t form < t life ---- Characteristic gas inflow rate to feed the cloud dM g /dt > M star /t life > 1 Mo/yr for M star >~ 10 6 Mo (Begelman 2008) HOW DO WE GET SUCH HIGH GAS INFLOW RATES AT < pc scales? Friday, August 17, 12
Recommend
More recommend
